1. Field of the Invention
The present invention relates to an IC card, and more particularly to an IC card with improved endurance against bending.
2. Description of the Related Art
Memory cards have been spreading rapidly as an external memory medium suitable for personal computers, multifunctional terminals, digital cameras, cellular phones, and portable audio players.
Multimedia cards standardized by MMCA (Multimedia Card Association), which is a standardization body, are widely known.
In those multimedia cards, as shown in FIG. 3 and FIG. 4, a substrate 102 carrying a memory is attached with an adhesive or the like to a card 100 made from a synthetic resin and having a size of a large postage stamp.
The structure of multimedia cards is disclosed, for example, in Japanese Patent Applications Laid-open No. 2003-50980, 2001-175835, and 2001-160125.
Japanese Patent Application Laid-open No. 2003-50980 describes that only the peripheral portion of the substrate is attached to the case with an adhesive or the like, and the problem associated with such a structure is that the bonding surface area of the peripheral portion of the substrate alone is small and when the case is bent, the substrate can easily peel off. Japanese Patent Application Laid-open No. 2001-160125 describes a similar structure, but no description relating to the substrate bonding method is provided.
Japanese Patent Application Laid-open No. 2001-175835 describes a structure in which a substrate is fitted into a recess in a case and joined thereto with an adhesive or the like. However, with such a configuration it is necessary, for example, to apply the adhesive by dropping into the recess and then to apply a pressure with a certain force from above to the substrate when the substrate is fitted into the recess.
The problem is, however, that with certain pressure application positions the substrate is tilted, a thin portion and a thick portion appear in the adhesive layer, and the bonding strength differs depending on location and is insufficient in the portion with a thin adhesive layer.
Furthermore, even if the pressure is uniformly applied to the substrate, if the applied pressure is too low, the substrate protrudes from the case surface and the thickness becomes outside of the range stipulated by the standard relating to IC cards. Conversely, if the applied force is too high, the adhesive escapes from the gap, the entire adhesive layer becomes thin, and the adhesive strength is sometimes insufficient.
Thus, within the framework of the conventional technology, various problems were associated with bonding a substrate by using an adhesive.
Further, the following problems were also associated with the conventional structure of IC cards.
Thus, when such a small IC card is inserted into a card slot, in most cases the user inserts the card by holding it between the fingers in the vicinity of the card center. In such cases, bending stresses act upon the IC card.
Japanese Patent Application Laid-open No. 2003-50980 describes the possibility of greatly reducing the production cost by making the substrate about half the size of the case.
However, if the substrate is about half the size of the case, the boundary of a thin portion where the substrate is disposed and a thick portion where the substrate is not disposed in the case is located in the vicinity of the case center in the insertion direction (see FIG. 3 of the aforementioned patent application). The problem is that if a flat case 100 such as shown in FIG. 5A is subjected to bending deformation as shown in FIG. 5B, then when the adhesive strength is insufficient, a substrate 102 peels off from a recess 104 into which the substrate 102 was fitted or, as shown in FIG. 5C, stresses concentrate in the vicinity of the end portion (close to the corner of the bottom portion of the recess 104), in the card center side, of the recess 104 into which the substrate 102 was fitted and a crack 106 appears therein.